If you are looking to buy a gun specifically for turkey hunting I would suggest using guns that are designed for just that ie: Mossberg 835/935, Remington 11-87, or what others there may be. When I went looking for a gun specifically for turkey, I was able to find a used Mossberg 835 for around $250 that had the mossy oak break up camo on it, tru glo fiber optic sights, and the factory choke.
If you have a used gun dealer in your area I am sure you can find a used Mossberg any where from $150-250. If your not partial to Mossberg I am sure you can find a quality Remington or any brand of gun for a decent price that is set up for turkey hunting. Then you wont have to worry about adjustable sights, buying a choke, or the barrel length.
Good luck to you!